If Szadek, Lord of Secrets would deal combat damage to a player, instead put that many +1/+1 counters on Szadek and that player puts that many cards from the top of his or her library into his or her graveyard.

If another effect would prevent Szadek’s combat damage from being dealt to the defending player or replace it with something else, that player chooses which effect applies first. For example, the player can choose to first have Mending Hands prevent 4 of the damage and then apply Szadek’s ability so that it gets only one counter.